linux-kernel - Re: [PATCH] panic.c: export panic_on

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 12 Oct 2009 13:48:03 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Simon Kagstrom <simon.kagstrom@...insight.net>,
	Artem Bityutskiy <dedekind1@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Koskinen Aaro (Nokia-D/Helsinki)" <aaro.koskinen@...ia.com>,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] panic.c: export panic_on_oops

On Mon, 2009-10-12 at 14:36 +0200, Ingo Molnar wrote:
> Well other than not using sleeping locks in that codepath it should be 
> properly serializable. If the serial driver, netconsole, fbcon and all 
> the other non-trivial console drivers can do it then MTD should be able 
> to do it too.

It's distinctly non-trivial. A 'real' user of the hardware may have just
triggered a block erase, which could take hundreds (or even thousands)
of milliseconds to complete. We can't always suspend that erase; do we
really want to _wait_ for it?

If we're actually in a _panic_ situation, then yes -- we want to wait,
and that's what the device driver's panic_write() method should do.

But for less critical output? I'm not so sure.

Of course, I'm currently looking at revamping the MTD APIs so they're
not entirely synchronous, and are queue-based like the block device API.
Then the console ->write() method could just queue the write, and we
need some other logic to ensure that it really does _happen_ when the
system crashes. A kind of 'purge queue of console writes' function in a
panic handler... except that as you point out, sometimes we actually
want that even when we haven't actually panicked.

-- 
dwmw2

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/